1. Field of the Invention
This invention relates to switching circuits.
2. Description of the Prior Art
In the context of this application, switching circuits are circuits employing electronic switching devices which comprise an element or a circuit that is primarily adapted for switching electrical signals in response to a control signal. Inverting switching devices are switching devices whose output signal is high when the control (input) signal is low, and vice-versa.
Electronic switching devices have long been used for switching of signals. Unlike ideal switches, however, electronic switching devices take a finite time duration to switch and dissipate energy during the switching time interval. This consumed power may become significant with respect to circuit operation and switch power dissipation capacity when switching durations are long and when switching repetition rates are high. To reduce this consumed and wasted power, high speed switching devices are generally employed.
The use of high speed switching devices, however, has a number of disadvantages. One, for example, is that high switching speeds induce large voltage and current transition rates (dv/dt and di/dt). The large transition rates cause noise to be radiated to the detriment of the immediate switching circuit and of the surrounding electronic apparatus. Another disadvantage is that high speed switching may cause a breakdown in the switching devices, especially when inductive loads are driven. In transistors this breakdown is called a secondary breakdown.
The high switching speed problems can be avoided by the use of only a moderately fast switching device, or by the slowing-down of a fast switching device by means of a capacitor connected between the device's output terminal and ground. With such slowing-down, however, the switching time of a device is still a function of the device's parameters, and of the slow-down capacitor's value. Thus, two switching devices would invariably have different switching times which, if interconnected in a push-pull center-tapped transformer configuration, would raise the possibility of both devices conducting simultaneously. Simultaneous conduction markedly increases the devices' power dissipation.